The shoulder forms a hard smooth roundness. But not impenetrable, really. In fact medial anterior humerus joined to glenoid fossa. Ball hugged gently, loosely by socket.

The shoulder arching towards the neck turns fleshy, firm: trapezius, the ornery muscle that buckles and knots under stress. A history of masseuses have kneaded the tucks and whorls of the tensed trapezius back to their original pliability, over and over again. No wonder—it supports the weight of the arm and restless head.

The shoulder becomes the taut story of collarbone meets neck, a fine swooping motion of the two clavicles. The clavicle, seen naked and unadorned, is eerily beautiful. Its double-arched curvature, described against the stark white of an instructional display, has the balance of fine pottery: ancient Grecian, perhaps, or porcelain Ming. Speculations say that the human clavicle shares roots with the weightless Y-shaped avian furcula, though speculations rarely say whether our evolutionary step was flight or fall. The clavicle, stripped free of its thin veneer of skin, taken from the context of its lumbering land-locked human body, looks exactly like a metaphor frozen in place: inhale, holding the air low and tense in your throat, and you will see your clavicles paired in graceful symmetry, straining against your skin, dropping and rising not like bones but like a wish.
The clavicle protrudes from the human anatomy. It juts from the thinnest, nestles deeper into the plumpest, but for most it carves as it curves a cradle, a safe space that gently—so gently for its apparent angularity—holds. The clavicle creates a depression that in turn becomes depository. Tears that stream from the cheeks, the chin, the face pressed against that bend where trapezius meets levator scapulae, the vertical muscle of the neck, roll with solemn gravity into this spot supported by the clavicles’ arches. So far, science has no name for it; it is, after all, too highly specialized, an anomaly really. Of all the species, only humans cry into it.

Science does have a name for the tender spot between the clavicles. Press your thumb to the hollow where the two bones end abruptly; press hard enough, and an uncomfortable suffocation mounts, your pulse beating in panic against the fleshy thumbpad. Relax. Here, unguarded by the vertical column of the sternum, is where the interclavicle should be. Now that the missing bone is preserved only in other branches of our common tree, interclavicle describes the emptiness left behind. The human take on the interclavicle feels, under probing fingers, like an oversight, a vulnerability that begs to be hidden behind a protective hand, or rib, or collarbone.
Birds have interclavicles fused with the furcula’s steadying shape, from which wings pivot in even arcs, the same beat over and over. Fish have free interclavicles; so do pigs, and cows, with their choppy, rocking gait. Look at your arms. Swing them, in wide-reaching circles, within their sockets. Humans have snubbed the path chosen by our four-footed friends, our fishy relatives, even the high-flying birds. A choice, perhaps originally a mistake, was made to shed the interclavicle’s small promise of protection for freedom of movement: the full motion of the dexterous arms and hands, the potential for elasticity that some gymnasts and dancers perfect. The trade seems fair enough.

II. A Cenozoic Fairy Tale

Once upon a time, in South America, right after the age of the dinosaurs (from which modern birds descend), a family of proto-bird predators ruled the land. Standing upright on deceptively bulky legs, fluttering still-stiff wings (the kinks out of which evolution hadn’t yet ironed), slashing with hooked beaks on whip-like necks, these Phorusraschids rushed to fill the missing link that the dinosaurs had left behind. Dinosaurs once hunted, killed, and ate other dinosaurs. But new times were coming 62 million years ago. What happened was a reshuffling of the food chain that put smallish, hairy, mammalian creatures on the menu.
Imagine: a new world order, one in which our cringing ancestors scuttled in fear and giant birds ruled with beaks like sledgehammers. This is the Cenozoic, the stage for the avian dream.
Scientists who unearthed the first Phorusraschidae fossils dubbed them the “terror birds,” which sounds funny when you first hear it. Not so much when you imagine the ten-foot-tall carnivores which won, and held, the title. Phorusraschids ruled their southern continent for millions of years as the watery gap dividing North and South America grew slimmer and slimmer—until finally, a land bridge emerged from the ocean and the giant birds moved across. Why they died out, no one knows. Perhaps it was climate that killed them; perhaps disease. It is more satisfying to imagine that they died in a way better suited to the way they lived, battling with—and losing to—furred, milk-bearing, warm-blooded creatures even more savage than they. Phorusraschids left behind one line of descendents, the seriemas. Little more than two feet long, seriemas are small, pretty birds with small, pretty beaks colored pink or orange. Their legs have become long and delicate, perfect for sprinting from danger, ill-suited for the long distance marathons of the hunt. Seriemas are often domesticated in modern day South America, used to guard chickens and eat small pests. But their eyes are sharp and watchful and hungry like a falcon’s. In the age of the seriema, the exhumation of a new Phorusraschid skull—more than two feet across, from a 300-plus pound specimen—is exciting and chilling all at once. To gaze through its huge, empty eye sockets is to imagine what Phorusraschid saw in its time, to wonder what old instincts might still slumber in its smaller cousins, and a window into an alternate world that, once upon a time, had the chance to be ours.

III. Portrait of the Anatomist as a Young Man

In 15th century Italy, a serious young man, a closeted and almost-convicted homosexual, a vegetarian philosopher and inventor, a bastard denied the legitimacy of his father’s last name and the darling of Renaissance world, drew the most beautiful and anatomically accurate depiction of a clavicle to ever be transcribed from thought to paper. His name was Leonardo da Vinci. He also invented the helicopter in 1490.
On the time-yellowed sheaf of the Vitruvian Man sketch, however, the clavicle recedes into the depression of the neck, then the shoulder, then the torso, the body. It is embedded, almost invisibly, as one of many perfect parts making a perfect whole. The end result is an image of the type that is impossible to see as anything other than complete: the perfect man, inscribed within the immutable arc of a beginningless, endless circle. His limbs point upward and outward, star-like; his image is the expression of a belief that the human body is a miniature, complete cosmos.
To view the Vitruvian Man, drawn in ink now indelible from ancient paper, is to believe—if only for as long as your eyes trace its lines—in the utter impossibility of chance evolution. To see it is to look into the deepest roots of Creationism, to see with your own senses the ineffable evidence that, once upon a time, perfection was conceived, was realized, was made unimproveable and unchangeable forever—and then you tear your gaze away, and the conclusion is once again your own to draw.
The Vitruvian Man is just one of many sketches in Leonardo da Vinci’s personal journals, which were released to the public piecemeal in decade- and century-long installments after his death. These glimpses into the mind of the greatest Renaissance man form a dense, furious slideshow of the fantastical and beautiful. Gargoyles, bridges, poems, birds’ wings stripped down to feather and bone, war machines, dissected plants, pages of draped cloth, ruminations on light, flying machines, and human bones, bodies, faces. Among his other accomplishments, Leonardo was also one of the earliest and most carefully documented anatomists. Dozens, hundreds of people remain preserved on paper. A look through his private musings reveals reams of distortions, perversions, and parodies of the human body laid out in the unforgiving, exquisite lines of a master artist’s work. And as you flip onward, the Vitruvian Man’s form fading, your starstruck eyes begin to adjust; you come to realize how very unearthly the beautiful proportions of that single sketch are, how very like Leonardo’s own improbable existence.
In truth, the Vitruvian Man was based on no living man. Realizing the hopelessness of modeling perfection from reality, Leonardo created it, instead, from a list of precise numbers and proportions laid out by a man who sanded stone free of flaws and shaped buildings, not people. Leonardo respected Classicists, men like the Roman architect Vitruvius. He admired the Greek system of philosophy and scientific thought. He was inspired, as were many artists of his age, by their colorful mythology. For all his greatness, he too, perhaps, liked to let his mind wander of a firelit evening, to think back on that fecund time of possibility: the age of Zeus, Athena, Hermes, Hercules, Perseus, Achilles. And Icarus.

IV. Anatomy, Part Deux

Simply by turning around, the shoulder becomes a completely different creature:

The shoulder, seen from the back, heaves like an ocean of skin and sinew. From this angle, edges are softened by the deltoideus muscle masking the shape of the bones and joint. The clavicle is hidden from sight, but it anchors the trapezius, which climbs over the midline and elongates into its namesake trapezoidal shape over the shoulder blades.
Shoulder blades are scapula; the hiss and thump of the sounds echo the bones’ flattened sharpness. Thin but insistent, blades surface against the muscled landscape to mirror the movement of the arms. Here is where description falters and observation takes its place. Simply watch, and patterns emerge slowly from the ebb and flow of action, relaxation.

V. Discrimination

Eaters covet the breast. The wing, the thigh, the dark juicy drumstick. They pooh-pooh the back. With complete disregard for the natural orientation of things, roasters happily flip the carcass of the chicken, or duck, or turkey or quail or pheasant in question, so that its back points panward and its underbelly points proudly toward the sky. So while the rest of the bird receives the royal treatment, painstakingly coaxed into a crackly golden-brown, the back is left to shrivel, blacken, and overcook.
Why ignore the back, which supports the burden of all that fleshy wealth, and, more to the point, is a hidden vein of rich marrow waiting to be cracked free? Part of the answer lies in a fundamental anatomical difference. Unlike gangly arms, which rely on the support of the back, avian biceps pull from the pectorals and the sternum—or, as we know them, the breasts. But another, larger, part of it is the abnormal plumping of chicken breasts everywhere, that, in the aftermath of a decade of the buttered, the canned, and the topped-with-Campbell’s-casseroles that permeated cookbooks from the post-war 1950s, heralded a new nutritional scramble for lower cholesterol. After decades of taste-preference training and fad diets, chicken cookers are now greeted with an obscenity of breast meat, far more than the amount really necessary for flight. Chicken eaters are stunned by surfeit.
Yet gnawers of hormone-free chickens and tasty wild game poultry suck every bit of meat from the bones, back included. (This is perhaps best experienced in a foreign KFC.) Breast discrimination does not happen when your entire bird is the size of a breast or two under the new-normal system.
These succulently coiffed and plumped breasts come from a less marvelous source. Imagine the chicken: the imbalanced underbelly that becomes undertow; the laughably inadequate legs and wings; the unruly cage-cramped feathers. Imagine the birds, as they used to be, as they could be: the wild pheasant, pre-domestication, elegant in its dusky plumage; the red-shouldered hawk, sleek of head and tail; yes, even the Phorusraschid, unchallenged apex predator during a glorious golden age. In the seemingly endless quest for more breast, less back, domesticated birds have been warped by the human imagination. We recreate them, god-like, in the image we want. But, though not bred for brains, do these birds ever waggle an underdeveloped wing, flex the weak muscles that once gifted flight, chafe under breasts that hang heavy from the spine, and dream?

VI. Of Birds and Men

The shoulder shares one more stranger connection, one that cannot be unearthed by a surgeon’s scalpel prying apart ligament and bone:
There is a fascination with human flight that has little to do with airplanes, and more to do with hang gliders and parasails. Icarus understood it, if you believe in him—and even if you don’t, he’s not the point. It’s the reason behind his downfall: a yearning to reach the sky without a motor.
An invisible, inseverable connection links human shoulders and wings, a tenuous wish threading through millennia. History has made the human wing, for all its intangibility, more real than serratus anterior, labrum, levator scapulae—because what are these to most of us but fuzzy abstracts? The stern Latin syllables conjuring up images less vivid, less deeply ingrained, less real than the familiar depiction of feathers sprouting from scapula? Our semicircular humeri, synovial membrane, manubrium, are words invented mere centuries ago for parts sometimes visible only under operating table lights; their hold on the human imagination is flimsy.
Not so angels. Legions of artists have painted, sculpted, and written angels to quasi-life, as if enough depictions piled one atop the other could finally round their flatnesses into full living glory. The angel is a deceptively simple concept: a perfect human body sprouting avian wings. Bird-man. Man-bird.
Yet the human anatomy at its best teeters, like most perfect things, on a precipitous balance. Harmonious precisely because there is no space, no spare muscle, no shelf of bone from which to hang an extra pair of feathered appendages. See how, in every imagining, the white wings drag almost to the ground—artists were practical enough, at the very least, to realize the wingspan needed to lift a cumbersome human body into the air. Yet the majestic span of these feathered behemoths would put an impossible strain on the shoulders. We would spend little time flying and much more massaging sore muscles that work doubletime, flexing wings and arms both. Were we more practical wishers, we would look to the four-limbed birds and accept that arms must be sacrificed for the gift of flight. Arms, wings, cannot be reconciled—
—but even the greatest genius born and raised amidst the intellectual luminance of the Renaissance spent spare moments sketching improbable designs for human flight. We are unwilling to compromise; we, like Icarus, are too greedy.
Examine carefully this dully aching want and see reason crumble. Because beyond the momentary beauty of feathers arching from flesh, what is there to prize in the unlikely hybrid of man and bird? Even to the ancient Zoroastrians who fathered the holy trinity of Judaism, Christianity, and Islam, winged fravashis were only guardians for mere mortal men, with never a role in their own right. Prized, above all, for their ability to parrot the words of another, simpletons disguised in brilliant plumage. “Birdbrain,” that old mocking truth—the flights of angels have never truly been their own.
But still—flight. The action that renders all thought inconsequential.
Man eats bird. Man contorts bird. Man chooses to walk a different evolutionary path from bird. Once upon a time, man feared bird. And, despite all, or perhaps because of it, man looks up, ever skyward, to envy the bird in flight.